The earlier M77's which are now called M77 Mark-I have the adjustable trigger and the tang safety.

About 1986 Ruger indroduced the new M77 Mark-II version. They did away with the adjustable trigger and the tang safety. Some of the earliest Mark II's still had the tang safetybut Ruger quickly switched over to the swing arm safety. All of the Mark-II's are marked Mark-II on the side of the receriver.